Tesla won't say so itself, but its much-discussed mainstream electric Model 3 appears to be powered by a battery about 11% smaller than the tiniest offered for its showcase luxury Model S, according to researchers who have gone to work figuring it out.

Vital news for battery fanatics: At a time researchers around the world are attempting to discover a breakthrough super-battery to bring electric cars to the masses, there is unusual interest in every detail about the $35,000 Model 3, which was launched July 28.

It's not clear why Tesla and CEO Elon Musk have been all-but silent about the battery, the car's most important spec, given that they have released at least bare-bones detail as a matter of course about its other vehicles. Tesla did not respond to emails from Axios about the battery.

But Venkat Viswanathan, a professor at Carnegie-Mellon University, said the car's 220-mile version appears to be powered by a 53.5 kWh battery, just smaller than the 60 kWh version in the smallest Model S battery. The Model 3's longer-range 310-mile version appears to have a 79 kWh battery. His findings — based on the general characteristics of the Model 3 that Tesla has released — generally jibe with estimates by some Tesla observers.

Update: Tesla's EPA certification, published today at Electrek, shows that Viswanathan's team estimate was spot on.

A surprise about the Model 3: "One really interesting point is that Model 3 has among the lowest drag coefficients of all passenger sedans, let alone in this price range," Viswanathan tells Axios. The drag coefficient — how easily the car can move through the wind — is measured at 0.23, compared with .24 for the Model S, which already had among the lowest.

Why it matters: The low drag coefficient means the car gets more energy out of a relatively small battery. And the smaller battery reduces the weight and price of the car, which is Musk's goal in attempting to create a big-selling mainstream electric.